Pain is associated with a variety of factors, and causes psychological distress to patients. Although appropriate pain-relieving treatments are available, there are still many types of pain that cannot be adequately controlled with currently available analgesic drugs or aids. Endothelin (ET), discovered as a potent vascular endothelium-derived vasoconstrictor, has been known to be involved in cardiovascular diseases. ET also causes pain, such as inflammatory, neuropathic and cancer pain via endothelin A receptors (ETAR), and has attracted attention in the field of pain. Further, ETAR antagonists have been reported to be involved in the enhancement of opioid analgesic effects and suppression of opioid tolerance; development of ETAR-targeted drugs as new analgesic treatments is much awaited. Here we report our knowledge of ET-1-induced pain and the relationship between ETAR antagonists and opioid analgesic signaling, and demonstrate the potential for a novel analgesic adjunct targeting for ETAR, together with our recent research.

Anterior cutaneous nerve entrapment syndrome (ACNES) is a known cause of chronic abdominal pain. We experienced a case of ACNES improved by an ultrasound-guided block. The patient was a 41-year-old man. He had persistent pain in the upper left abdomen was diagnosed with ACNES and visited our department. Ultrasound image revealed an high-intensity region in the rectus abdominis muscle. Immediately after performing the modified thoraco abdominal nerves through perichondrial approach block (m-TAPA block), the pain improved with NRS 4 to 0/10. In addition, mepivacaine and dexamethasone was injected around the high-intensity region. No recurrence of symptoms was observed even after one and a half months. The high-intensity region in image was the strangulation part of the anterior cutaneous branch of the intercostal nerve that caused ACNES. Both ultrasound guided trigger point block and m-TAPA block were contributed to the improvement of abdominal wall pain.

Microvascular decompression (MVD) is the radical treatment for trigeminal neuralgia; however, some patients experience recurrence of pain after MVD. Here we report a case of recurrent trigeminal neuralgia after MVD in a young woman who was successfully treated with a postoperative maxillary nerve block by pulsed radiofrequency. The patient, a woman in her 30s, underwent MVD for paroxysmal pain in the area of the second division of the left trigeminal nerve. She experienced pain recurrence in the same area 6 months after surgery. Radiofrequency thermocoagulation performed in the left infraorbital nerve alleviated the pain temporarily; however, soon thereafter, pain in the left posterior oral region increased. Ultrasound-guided maxillary nerve pulsed radiofrequency ultimately resolved the pain. These results suggest that ultrasound-guided maxillary nerve pulsed radiofrequency is useful for the treatment of recurrent trigeminal neuralgia after MVD since it can be performed safety and is associated with few complications.